The brain is so complex that most of what we know of its workings comes from understanding what happens when things go wrong. It is for this reason that neurologists are fascinated by what they term "deficits". Deficits occur where a part of the brain is damaged and a person's behaviour or abilities are altered as a result. In The Man Who Mistook His Wife for a Hat, Oliver Sacks tells the stories of a number of individuals who, as a result of brain damage, are afflicted with fantastic perceptual and intellectual aberrations. While strange and fascinating, these tales could quite easily be uncomfortably voyeuristic if it were not for the sympathetic and deeply human way in which Sacks recounts them.

Through these incredible tales, we are able to glean an insight into the world of the neurologically impaired, a world in which many of the things we take for granted become major challenges. For example, the book takes its title from the case of a man who could recognise inanimate objects and abstract shapes perfectly well, but on leaving Sacks' office, he attempted to put his wife's head on top of his own, believing it to be his hat.

Although not specifically about the architecture and functional specialities of the various regions of the brain, the book alludes to them by identifying the symptoms patients suffer as a result of damage to specific parts of the brain. For example, in the chapter entitled "Eye's Right!" a woman who had suffered a massive stroke in her right cerebral hemisphere completely lost the concept of "left". She would often complain to the nurses that they had forgotten to serve a drink with her meal, but when they said "it's there, on the left side of your tray", she would simply look confused. She would also complain that the portions of food she was served were too small, yet she would only eat the food from the right side of her plate.

Further into her recovery from the stoke, Sacks worked with her to develop strategies to cope with her missing left. Fortunately her intelligence was not impaired so she was well aware of the absurdity of her situation but unable to overcome it. Perhaps the most bizarre aspect of the story is that when she put make-up on, she would only apply it to the right side of her face - "I look in the mirror" she said "and do all I see". As a solution they tried using a video system to act as a form of mirror that would display her left side on the right. Interestingly, when first shown this she cried "take it away!" as, since the stroke, the left side of her face and body had no feeling or existence for her.

Apart from describing the strange afflictions of his subjects, Sacks uses the book to demonstrate how people with deficits in one area often have strengths in others. For example, he tells the story of a pair of 26 year old twins. They had an IQ of just 60 and were severely limited in many ways yet had a great gift for numbers. They had become famous for being able to instantly tell you the day of the week for any date that you chose to mention, and when Sacks accidentally dropped a box of matches on the floor, they both instantly shouted "111", they then murmured "37, 37, 37". When Sacks counted the matches there were indeed 111. "How did you count them so quickly" Sacks asked. "We didn't count" they said "we saw 111."

By highlighting the positives, Sacks provides a wonderful insight into the way in which the human mind is able to find strength in adversity.